It was something of a head scratcher when it was announced that Foo Fighters frontman Dave Grohl would be playing with Zac Brown Band on last month’s CMA Awards. But the resulting collaboration between the former Nirvana drummer and the Southern rockers on the proggy, swampy “Day for the Dead” ended up being one of the most electric of the evening. Now comes this four-song EP, available Tuesday on iTunes, that proves that it could be an even more fruitful partnership. Alongside a recorded version of “Day for the Dead,” which further expands the group’s reach into jam band territory, the EP includes a richly layered cover of the Wood Brothers’ smoky heartbreaker “The Muse” and the Southern gospel charmer “All Alright,” which features a liquid molten slide guitar solo courtesy of A.J. Ghent. In addition to producing the set with an ear for warmth, Grohl plays drums on “Let It Rain” which definitely gives the band some extra snap. And the group’s signature harmonies are lush throughout. Given the title, we look forward to a possible “Vol. 2.” (Out Tuesday)